Communication and homeostasis

Define stimulus

A stimulus is any change in the environment that causes a response.

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Define response

A response is a change in behaviour or physiology as a result of a change in the enviroment.

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Define homeostasis

The maintenance of a constant internal environment despite external changes.

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Define negative feedback

A process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis.

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Outline negative feedback

A change away from optimum conditions occurs. Receptors detect the change. Communication system informs effector. Effector reacts to reverse change. Return to optimum conditions.

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Define positive feedback

A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis.

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Outline positive feedback

A change away from optimum conditions occurs. Receptors detect change. Communication system informs effector. Effector reacts to increase the change.

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Define ectotherm

An ectotherm is an organism that relies on external sources of heat to regulate its body temperature.

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List 3 advantages of being an ectotherm.

1.Use less of their food in respiration. 2.They need to find less food and may be able to survive for long periods of time without eating. 3.A greater proportion of the energy obtained from food can be used for growth.

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List 2 disadvantages of being an ectotherm.

1.Less active in cooler temperatures this puts them at a greater risk of predation. 2.May not be capable of activity during the winter as they never warm up sufficiently they must have sufficient stores of energy to survive over winter without eating

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Outline the temperature regulation in ectotherms

When cold they will change their behaviour or physiology to increase absorption of heat from their environment. When cold they will change their behaviour or physiology to decrease absorption of heat and increase heat loss to its enviroment.

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How does exposing their body to the sun help to regulate temperature?

Enables more heat to be absorbed. E.g. Snakes

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How does orientating their body to the sun help to regulated temperature?

Exposes larger surface area for more heat absorption. E.g. Locus

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How does orientating their body away from the sun help to regulate body temperature.

Exposes a lower surface area so less heat is absorbed. E.g. Locus

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How does hiding in a burrow regulate body temperature?

Reduces heat absorption by keeping out of the sun. E.g. Lizards

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How does altering body shape regulate body temperature?

Exposes more or less surface area to the sun. E.g. Horned lizards

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Hiow does increasing breathing movements regulate body temperature?

Evaporates more water. E.g. Locus

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Define endotherm

An endotherm is an organism that can use internal sources of heat to maintain its body temperature.

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List 3 advantages of being an endotherm.

1.A fairly constant body temperature whatever the temperature is externally. 2.Activity possible when external temperatures are cool. 3.Ability to inhabit colder parts of the planet.

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List 3 disadvantages of being an endotherm.

1.A significant part of the energy intake is used to maintain body temperature in the cold. 2.More food required. 3.Less of the energy from food is used for growth.

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What is the response of the sweat glands if the core body temperature is too high?

Secrete more seat onto skin; water in sweat evaporates, using heat from blood to supply latent heat of vaporisation.

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What is the response of the sweat glands if the core body temperature is too low?

Less sweat is secreted; less evaporation of water, so less loss of latent heat.

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What is the response of the lungs, mouth and nose if core body temperature is too high?

Panting increases evaporation of water from lungs, tongue and other moist surfaces, using latent heat.

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What is the response of the lungs, mouth and nose if core body temperature is too low?

The animal does not pant, less water evaporates.

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What is the response of the hairs on skin if the core body temperature is too high?

Hair lie flat, providing little insulation, and thus more heat can be lost by convection and radiation.

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What is the response of the hairs on skin if the core body temperature is too low?

Hairs are raised to trap a layer of insulating air, reducing the loss of heat from the skin.

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What is the response of the arterioles leading to capillaries in the skin if the core body temperature is too high?

Vasodilation allows more blood into the capillaries near the skin surface; more heat can be radiated from the skin.

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What is the response of the arterioles leading to the capillaries in the skin if core body temperature is too low?

Vasoconstriction reduces the flow of blood through capillaries near the surface of the skin; less heat is radiated.

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What is the response of the liver cell if core body temperature is too high?

Rate of metabolism is reduced; less heat is generated from exergonic reactions such as respiration.

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What is the response of the liver cells if core body temperature is too low?

Rate of metabolism is increased, therefore respiration generates more heat, which is transferred to the blood.

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What is the response of the skeletal muscles if core body temperature is too high?

No spontaneous contractions.

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What is the response of the skeletal muscles if core body temperature is too low?

Spontaneous contractions (shivering) generates heat as muscle cells respire more.

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Outline the control of temperature regulation in an exotherm if there is a rise in core temperature

Thermoregulatory centre in the hypothalamus detects change. Nervous system, and hormonal system carry signals to skin, liver and muscles. Less heat generated and more heat loss. Temperature falls.

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Outline the control of temperature regulation in an exotherm if there is a fall in core temperature.

Thermoregulatory centre in the hypothalamus detects change. Nervous system and hormonal system carry signals to skin, liver and muscles. More heat generated and less heat lost. Temperature rises.

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What are sensory receptors?

Specialised cells that can detect changes in our surroundings. They are energy transducers that convert one form of energy into another.

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What is a polarised membrane?

A polarised membrane is one that has a potential difference across it. This is the resting potential.

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Outline generating a nerve impulse.

A nerve impulse is generated by altering the permeability of the nerve cell membrane to sodium ions. As the sodium ion channels open the membrane permeability increases and sodium ions move across the membrane down their concentration gradient into

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How is a polarised membrane maintained?

Sodium/potassium ion pumps actively transport sodium ions out of the cell and potassium ions into the cell. More sodium ions are actively transported out of the cell than potassium ions that are actively transported into the cell.

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Define generator potential

A generator potential is a small depolarisation caused by sodium ions entering the cell.

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Define depolarisation

Depolarisation is the loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.

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What is the role of a sensory neurone?

Sensory neurones carry the action potential from a sensory receptor to the CNS.

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What is the role of a motor neurone?

Motor neurones carry the action potential from the CNS to an effector.

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What is the role of a relay neurone?

Relay neurones connect sensory and motor neurones.

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List 9 features of neurones

1.Many are very long so that they can transmit the action potential over a long distance. 2.The cell surface membrane has many gated ion channels that control the entry or exit of sodium, potassium or calcium ions.

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Define resting potential

The resting potential is the potential difference or voltage across the neurone cell membrane while the neurone is at rest. It is about -60mV inside the cell compared with the outside.

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What is happening within a resting neurone to maintain a resting potential?

It is actively transporting ions across its cell membrane. Soduim/potassium ion pumps use ATP to pump 3 sodium ions out of the cell and 2 potassium ions in. The plasma membrane is more permeable to potassium ions than to sodium ions and many diffuse

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What is the value of the resting potential?

-60mV

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What is a voltage-gated channel?

voltage-gated channels are channels in the cell membrane that allow the passage of charged particles or ions. They have a mechanism called a gate which an open and close the channel. In these channels the gates respond to changes in the potential

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Define threshold potential.

The threshold potential is a potential difference across the membrane of about -50mV. If the depolarisation of the membrane does not reach the threshold potential then no action potential is created.

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Define action potential

The action potential is a depolarisation of the cell membrane so that the inside is more positive than the outside; with a potential difference across the membrane of +40mV

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Why is the action potential described as an all or nothing response?

A neurone either conducts an action potential or it does not.

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How is an action potential generated?

1.The membrane starts at the resting potential -60mV. It is polarised. 2.Sodium ion channels open and some sodium ions diffuse into the cell. 3.The membrane depolarises and reaches the threshold value of -50mV.

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What is the refractory period?

The short period of time after firing during which it is impossible to stimulate the cell membrane to reach another action potential.

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What is the purpose of the refractory period?

Allows the cell to recover after an action potential. It also ensures that action potential are only transmitted one way.

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Define local currents

Local currents are the movement of ions along the neurone. The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration.

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Outline how local currents are produced.

An action potential occurs opening the sodium ion channels at a particular point along the neurone, this allows sodium ions to diffuse across the membrane from the region of higher concentration outside the neurone into the neurone.

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Outline the role of voltage-gated sodium ion channels in the transmission of action potentials.

The local current alters the potential difference across the membrane. When the potential difference across the membrane is reduced the gates open allowing sodium ions to enter the neurone at a point further along the membrane. The action potenital

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Define saltatory conduction

Saltatory conduction refers to the way that the action potential appears to jump from one node of Ranvier to the next.

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Where do the ionic exchanges that cause an action potential occur?

The nodes of Ranvier

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What is a neurotransmitter?

A neurotransmitter is a chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.

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What is a cholinergic synapse?

Cholinergic synapses are those that use acetylcholine as their transmitter substance.

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What is the synaptic knob?

A swelling at the end of the presynaptic neurone.

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List 4 specialised features of the synaptic knob.

1.Many mitochondria - indicating that an active process, needing ATP, is involved. 2.A large amount of smooth endoplasmic reticulum. 4.Vesicles of acetylcholine, the transmitter substance that will diffuse across the cleft.

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Describe the postsynaptic membrane

Contains specialised sodium ion channels that can respond to acetylcholine, they consist of 5 polypeptide molecules, 2 of which have a special receptor site that is specific to acetylcholine, they have a complementary shape and will bind with

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Describe the transmission across the synapse.

An action potential arrives at the synaptic knob. The voltage-gated calcium ion channels open. Calcium ions diffuse into the synaptic knob causing the synaptic vesicles to move and fuse with the presynaptic membrane. Acetylcholine is released by

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Define acetylcholinesterase

An enzyme in the synaptic cleft that breaks down the transmitter substance acetylcholine.

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Outline the role of acetylcholinesterase

It hydrolyses the acetylcholine to ethanoic acid and choline stopping the transmission of signals so that the synapse doesn't continue to produce action potentials in the postsynaptic neurone. The ethanoic acid and choline are recycled and re-enter

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Define summation.

Summation is a term that refers to the way that several small potential changes can combine to produce on larger change in potential difference across the membrane.

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List 7 roles of synapses in the nervous system

Several presynaptic neurones might converge to one postsynaptic neurone - this allows signal from different parts of the nervous system to create the same response. 2.One presynaptic neurone might diverge to several postsynaptic neurones - allows one

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What is the advantage of mylination?

Mylinated neurones can transmit an action potential much more quickly that non-myelinated neurones.

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Describe the differences between myelinated and non-myelinated neurones.

Myelinated neurones are longer and carry signals over longer distances. Myelinated neurones carry signals from sensory receptors to the CNS and from the CNS to effectors. Non-myelinated neurones are used in coordinating body functions.

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Define hormones

Molecules that are released by endocrine glands directly into the blood. They act as messengers carrying a signal from the endocrine gland to a specific target organ or tissue.

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What is an endocrine gland

An endocrine gland is a gland that secretes hormones directly into the blood. Endocrine glands have no ducts.

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What is an exocrine gland?

An exocrine gland is a gland that secretes molecules into a duct that carries the molecules to where they are used.

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What are target cells?

Target cells are those that possess a specific receptor on their plasma membrane. The shape of the receptor is complementary to the shape of the hormone molecule. Many similar cells together form a tissue.

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What are the two types of hormones and how do they work?

1.Protein and peptide hormones - not soluble in the phospholipid membrane and don't enter the cell. 2.Steroid hormone - can pass through the membrane, into the cell and have a direct effect on the DNA in the nucleus.

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What is adrenal cyclase?

An enzyme associated with the receptor for many hormones, including adrenaline. It is found on the inside of the cell surface membrane.

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Outline the action of adrenaline

Adrenaline in the blood binds to its specific receptor on the cell surface membrane, the adrenaline molecule is the first messenger. When it binds to the receptor it activates adenyl cyclase which converts ATP to cyclic AMP, the cAMP is the second

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What does the adrenal medulla manufacture?

Adrenaline.

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List 9 effects of adrenaline.

1.Relax smooth muscle in the bronchioles. 2.Increase stroke volume of the heart. 3.Increase heart rate. 4.Cause general vasoconstriction to raise blood pressure. 5.Stimulate conversion of glycogen to glucose. 6.Dilate the pupils.

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What does the adrenal cortex do?

Uses cholesterol to produce certain steroid hormones.

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What are the roles of steroid hormones?

1.Mineralocorticoids help to control the concentration of sodium and potassium in the blood. 2.Glucocortiods help to control the metabolism of carbohydrates and proteins in the liver.

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Describe the exocrine function of the pancreas.

The majority of cell s in the pancreas manufacture and release digestive enzymes. The cells are found in small groups surrounding tiny tubules into which they secrete digestive enzymes. The tubules join to make up the pancreatic duct.

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Describe the endocrine function of the pancreas.

The islets of Langerhans contain alpha cells that manufacture and secrete glucagon, and beta cells that manufacture and secrete insulin. the islets secrete the hormones directly into the blood.

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What is the pancreatic duct?

A tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine.

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Where are the alpha and beta cells found?

In the islets of Langerhans.

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What do alpha cells secrete?

Glucagon

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What do beta cells secrete?

Insuline

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What is insulin?

The hormone released from the pancreas that causes blood glucose levels to go down.

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What is glucagon?

The hormone that causes blood glucose levels to rise.

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What are the islets of Langerhans?

Small patches of tissue in the pancreas that have an endocrine function.

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What happens if blood glucose rises too high?

A high blood glucose concentration is detected by the beta cells, in response they secrete insulin into the blood, which targets hepatocytes, muscles cells and other body cells that possess specific membrane bound receptors for insulin. When the

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What are hepatocytes?

Hepatocytes are liver cells. They are specialised to perform a range of metabolic functions.

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What happens if blood glucose drops too low?

A low blood glucose concentration is detected by the alpha cells, in response they secrete glucagon. Its target cells are the hepatocytes which possess the specific receptor for glucagon. 1.Conversion of glycogen to glucose occurs (glycogenolysis)

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Outline the control of insulin secretion.

1.The cell membrane of the beta cells contain both calcium ion channels and potassium ion channels. 2.The potassium ion channels are normally open and the calcium ion channels are normally closed. Potassium ions diffuse out of the cell making the

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What is diabetes mellitus

A disease in which blood glucose concentrations cannot be controlled effectively.

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What is hyperglycaemia?

The state in which the blood glucose concentration is too high.

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What is type I diabetes?

Insulin-dependent diabetes that usually starts in childhood. The body is no longer able to manufacture sufficient insulin and cannot store excess glucose as glycogen.

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What is type II diabetes?

Non-insulin dependent diabetes. A person with type II diabetes can still produce insulin but there responsiveness to insulin declines. The levels of insulin secreted by the beta cells may also decline.

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What is hypoglycaemia?

The stae in which the blood glucose concentration is too low.

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How is type II diabetes treated?

Carefully monitoring and control of diet which may be supplemented by insulin or other drugs.

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How is type I diabetes treated?

Insulin injections. The blood glucose concentration must be monitored and the correct does of insulin administered to ensure that the glucose concentration remains fairly stable.

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What is cell metabolism?

The result of all the chemical reactions taking place in the cytoplasm.

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List 3 ways the heart adapts to supply more glucose and oxygen?

1.Increases the number of beats per minute. 2.Increases the strength of contractions. 3.Increases the stroke volume.

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List 4 factors that affect the heart beat.

1.The hear muscle is myogenic. 2.The heart contains its own pacemaker. 3.The heart is supplied by nerves from the medulla oblongata of the brain which can control the SAN frequency. 4.The heart muscles respond to the presence of adrenaline.

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Communication and homeostasis

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